1. Field of the Invention
The present invention relates to a magnetism detecting device which makes use of a magnetic impedance effect, a magnetism sensor using the magnetism detecting device, and a terrestrial-magnetism detecting azimuth sensor and an attitude controlling sensor both of which use the magnetism sensor.
2. Description of Related Art
A conventional general type of terrestrial-magnetism detecting azimuth sensor (hereinafter referred to as the azimuth sensor) is a flux gate sensor. This sensor includes an easily saturable annular core around which an exciting coil is toroidally wound, and a pair of detecting coils disposed in such a manner as to intersect at right angles to each other above the annular core. The sensor obtains a vector quantity from two horizontal components of force and detects an azimuth angle.
However, the fluxgate sensor cannot be reduced in size, and needs an exciting current so that a magnetic element can be used in a saturated state. Accordingly, if such a fluxgate sensor is to be incorporated into portable equipment, the fluxgate sensor cannot be reduced in size beyond a certain limit.
For these reasons, a magnetism detecting device (hereinafter referred to as the MI device), disclosed in Japanese Laid-Open Patent Application No. Hei 7-181239, which makes use of a magnetic impedance effect due to amorphous wire has recently become known. The magnetic impedance effect is the phenomenon in which if a high-frequency current of MHz frequency band flows through a magnetic element, the impedance of the magnetic element varies due to an external magnetic field so that the amplitude of the voltage across the magnetic element varies up to some tens of percent due to a small magnetic field of approximately several gausses. This MI device has a detection sensitivity equal to that of the fluxgate sensor and can be applied to an azimuth sensor. An application of the MI device to the azimuth sensor is stated in "Colpitts Oscillation Type of Magnetism Microsensor Using Amorphous-Wire MI Device" announced at a lecture to the 18th meeting of The Japan Society of Applied Magnetics (14pB-7).
The arrangement of this azimuth sensor is such that an amorphous wire is incorporated in a Colpitts oscillator so that a variation in an external magnetic field appears as a variation in an oscillation amplitude and the variation in the oscillation amplitude is provided as an output from an envelope detecting circuit. Incidentally, to discriminate between south and north, a direct-current bias magnetic field is applied to the device by causing a direct current to flow through a coil directly wound around the wire of the device.
However, to put the aforesaid azimuth sensor into practice, it is considered to be necessary to solve problems which will be stated below.
1) Amorphous wire makes it difficult to mount an oscillator on a printed circuit board by direct soldering. In addition, since amorphous wire is easily bent, handling is difficult in terms of maintainability of its straight shape and the like.
2) Since a variation in the absolute value of an amplitude voltage of an oscillation circuit is handled as a sensor output, the sensor output is susceptible to amplitude variations due to variations in source voltage or the temperature characteristics or the like of other electrical elements.
3) Since terrestrial magnetism is weak, a variation in a detected signal is as small as several percent and is susceptible to noise.
4) Fine adjustment of the oscillation amplitude is needed, and it is difficult to adjust X- and Y-axis sensitivities to each other.